Struct constructor, opCall mess.

[Remo]

> Fortunately?
Yes I think it is. Of course it could be made a more safe in some 
way.

I think the big advantage of D is that it has 'bridge' to C and 
C++.
This way it appears to be easy to port some C++ code to D.
And it appears to be easy to interconnect C++ and D code. (via 
Dll for example)

> @disable this()
Yes this is possible.
But then why it is not possible to use something like this ?
@default this();

For Vector example this works pretty well this way.
But my main problem is more complicated.

extern(C)  int init(ref CWrapper p);
extern(C) void free(ref CWrapper p);

struct CWrapper
{
   //some data that must be the same at C side.
   Data m_data;

   this() {
      init(&this);
   }
   ~this() {
      free(&this);
   }
}

How to do something like this in D ?
Using class appears for me to be wrong direction.


On Monday, 24 February 2014 at 18:13:02 UTC, Stanislav Blinov 
wrote:
> On Monday, 24 February 2014 at 17:15:10 UTC, Remo wrote:
>
>> Well fortunately it seems to be possible to override init 
>> property.
>
> Fortunately? I think not. It's an abomination that, IMO, has to 
> be annihilated. Recently Andrei suggested adding more explicit 
> semantics to .init that may give some leeway in this matter, 
> although this was concerning classes and non-null default 
> values, so it may not concern structs at all. Regardless, my 
> advice - don't try to override .init, i.e. don't invite trouble 
> into your code :)
>
>> But it still does not called at struct construction.
>> http://melpon.org/wandbox/permlink/9EvcdzKUKoufqbJa
>
> Yup.
>
>> So what is proper/best way to mimic default constructor for 
>> struct ?
>
> Don't do it. Default construction for struct *is* 
> initialization of its fields.
> If you want to do something other that initialize fields - 
> create a function and call it explicitly. D is not C++, don't 
> expect it to behave identically. To make it easier when porting 
> code, you can always temporarily @disable this() so the 
> compiler will stop whenever you'd use your "special" default 
> construction in C++.
>
> As you've mentioned, the code from your example doesn't need 
> any special default constructors at all, this will work just 
> fine:
>
> struct Vector(T) {
>     T x = 0, y = 0, z = 0;
>
>     this(T v) { x = y = z = v; }
>     this(T x, T y, T z) { this.x = x; this.y = y; this.z = z; }
> }
>
>
> unittest {
>     Vector!double v;
>     auto v2 = Vector!double(1);
>     auto v3 = Vector!double(1,2,3);
>
>     assert(v.x == v.y && v.y == v.z && v.z == 0);
>     assert(v2.x == v2.x && v2.y == v2.z && v2.z == 1);
>     assert(v3.x == 1 && v3.y == 2 && v3.z == 3);
> }
>
>
> Also please take a look at those:
>
> https://d.puremagic.com/issues/show_bug.cgi?id=3438
> https://d.puremagic.com/issues/show_bug.cgi?id=6080
> https://d.puremagic.com/issues/show_bug.cgi?id=7066
> https://d.puremagic.com/issues/show_bug.cgi?id=7597
> https://d.puremagic.com/issues/show_bug.cgi?id=8816
> https://d.puremagic.com/issues/show_bug.cgi?id=8817
> https://d.puremagic.com/issues/show_bug.cgi?id=10413
> https://d.puremagic.com/issues/show_bug.cgi?id=11307
>
> There may be some others I've missed; the sheer amount and 
> unresolved state is terrifying.